Which technique shall be utilized to establish elevations on the required project control points?

• A. Differential leveling
• B. Trigonometric leveling
• C. GPS leveling
• D. Photogrammetric leveling

Answer: (A)

Differential leveling is the technique used for establishing elevations on required project control points because it directly measures vertical differences between points with high precision. By using a precise leveling instrument and graduated staff, surveyors determine the change in height from one point to the next along a sequence, which minimizes cumulative errors and ties all control points to a common vertical datum. This method is the standard for vertical control in construction projects due to its reliability, repeatability, and ability to achieve tight elevation tolerances.

Other methods have limitations for this purpose. Trigonometric leveling relies on angles and distances to infer height differences and can be affected by refraction, curvature of the Earth, and distance errors, making it less robust for a network of control points. GPS leveling (GNSS-based vertical positions) provides elevations relative to a geodetic datum, but translating to a precise local vertical datum and achieving high accuracy across multiple points can be more complex and less reliable for strict construction-grade elevation control. Photogrammetric leveling derives elevations from imagery, which is indirect and depends on photo quality, model accuracy, and terrain features, not as straightforward or precise for establishing direct elevations at control points.